The present invention relates to a rechargeable battery configured in the form of a battery pack in which a plurality of cells are connected so as to obtain the required electrical capacity, and more particularly to a rechargeable battery in which the heat radiation of the battery pack is enhanced and there is less temperature differential between cells, so that charging efficiency is equalized and there is no variance in the battery capacity of the various cells.
A conventional rechargeable battery constructed such that the required electrical capacity is obtained by connecting and integrally linking a plurality of cells into a battery pack is structured as shown in FIG. 16, for example. This rechargeable battery is an example of a battery pack made up of sealed alkaline rechargeable batteries, and the cells 1a to 1j that make up this battery pack are constructed as shown in FIG. 15.
In FIG. 15, the cell 1 is constructed such that a group of electrode plates 7, comprising positive and negative electrode plates layered with separators between them, is housed in a battery housing 2 along with electrolyte, the opening in the battery housing 2 is closed off with a cover 6 provided with a safety vent 5, and a positive electrode terminal 3, which is connected to leads taken from the positive electrode plates of the group of electrode plates 7, and a negative electrode terminal 4, which is connected to leads 9 taken from the negative electrode plates, are attached to the cover 6.
When the battery pack is put together, as shown in FIG. 16, the plurality of cells 1a to 1j are abutted against each other between the long (wide) sides of the battery housings 2, and the end plates 32, which are abutted against the outsides of the battery housings located at the ends, are bound together with binding bands 33 to integrally link the cells 1a to 1j. The positive electrode terminals 3 and negative electrode terminals 4 between linked adjacent cells 1 are connected by connector plates 31, and the cells 1 are connected in series. When the battery housings are linked, ribs 8 formed vertically on the long sides of the battery housings 2 are aligned with the ribs 8 on the adjacent battery housings 2, forming coolant passages that open above and below the battery housings 2 between the paired ribs 8.
A rechargeable battery generates joule heat and reaction heat through the chemical reaction that accompanies charging and discharging. The greater is the electrical capacity, the more heat is generated, and if the battery is sealed, the radiation of heat to outside the battery is slowed and even more heat builds up inside the battery, so when a battery pack with a large electrical capacity is made up of sealed rechargeable batteries, it is essential to provide some means for the efficient radiation of the heat that is generated. With the conventional rechargeable battery structure shown in FIG. 16, the coolant passages are formed by the ribs 8 between adjacent cells 1 as mentioned above, so heat generated by the cells 1 can be effectively radiated by forcing a coolant such as air through these coolant passages. A heat radiation structure such as this is disclosed in Japanese Laid-Open Patent Application No. 3-291867.
Nevertheless, when a battery pack is produced by arranging cells as in this conventional structure, a problem is that the greater is the number of cells 1 arranged, the greater is the temperature differential between the cells 1 located toward the middle and the cells 1 located on the outer ends. With the conventional structure shown in FIG. 16, the cells 1a and 1j located on the outer ends are less subjected to the effects of the heat generated by the other cells 1, and the end plates 32 also carry away some of the heat, so these cells are under good thermal radiation conditions. The closer a cell 1 is to the middle, the more it is affected by the heat generated by the cells 1 to either side, so the temperature rises more and heat radiation is not as good. Consequently, with a conventional structure, the closer a cell 1 is to the middle, the worse its heat radiation conditions are, the result being a temperature differential in which the temperature of the cells 1a to 1j is lower toward outside and higher toward the middle.
The charging efficiency of a rechargeable battery is affected by the temperature thereof, so if there is a temperature differential between the cells that make up the battery pack, as with a conventional structure, there will be a difference in the electrical capacity of the various cells. With a battery pack in which cells whose capacity thus varies are connected in series, those cells with lower capacity are in a state of overdischarge at the end of discharge. Repeated charging and discharging in this state in which there is a difference in the capacity of the cells shortens the cycling life of a battery pack and leads to diminished dischargeable capacity.
It is an object of the present invention to provide a rechargeable battery with enhanced performance as a battery pack, with no temperature differential between the cells that make up the battery pack.
The rechargeable battery according to a first aspect of the present invention for achieving the above object is characterized in that a battery housing containing elements for electromotive force of a cell is formed in a rectangular shape having short sides with a narrow width and long sides with a wide width, and a plurality of cells are linked together adjacent to one another between the short sides of this battery housing to form a battery pack with a required electrical capacity.
With the structure of this rechargeable battery, the plurality of cells that make up the battery pack are arranged in a single row with the short sides of the battery housings next to each other, so the long sides of the cells all face outward and the temperature environment thereof is equalized, resulting in an extremely small temperature differential between the cells. Therefore, there is also less difference in charging efficiency, which varies with the battery temperature, and there is no variance in the cell capacity, so none of the cells is overdischarged during discharging, and the cycling life of the rechargeable battery can be kept long.
The rechargeable battery according to a second aspect of the present invention for achieving the above object is characterized in that a battery housing containing elements for electromotive force of a cell is formed in a rectangular shape having short sides with a narrow width and long sides with a wide width, a plurality of cells are linked together adjacent to one another between the short sides of their battery housings to form battery modules, these battery modules are arranged in parallel in a plurality of rows adjacent to one another between the long sides of the battery housings, and the plurality of rows of battery modules are linked together to form a battery pack with a required electrical capacity.
With the structure of this rechargeable battery, the plurality of cells that make up the battery pack are arranged in a single row with the short sides of the battery housings next to each other, thus forming a battery module, and these battery modules are arranged in parallel in a plurality of rows, so the long sides of the cells face outward and the temperature environment is equalized, resulting in an extremely small temperature differential between the cells. Therefore, there is also less difference in charging efficiency, which varies with the battery temperature, and there is no variance in the cell capacity, so none of the cells is overdischarged during discharging, and the cycling life of the rechargeable battery can be kept long. It is also possible to increase the number of battery modules linked or shorten the linkage length by further disposing in parallel battery modules linked on the short sides.
In the above structure, if a heat transfer plate with good thermal conductivity is provided between the battery modules disposed in parallel, then the heat between the sides facing each other in parallel, where the long sides of the battery housings are next to each other and heat radiation is not as good, can be exchanged to the heat transfer plate, and the temperature can be kept from rising between sides facing each other in parallel where heat radiation is not as good.
Also, if a heat transfer plate with good thermal conductivity is provided between the battery modules disposed in parallel, and if end heat transfer plates exposed to the outside of the plurality of integrated cells are linked to the ends of this heat transfer plate in the direction in which the battery modules are linked, then the heat of the heat transfer plate, the temperature of which is increased through heat exchange, can be radiated from the end heat transfer plates exposed to the outside.
Active cooling via a heat exchanger is also possible by making a coolant flow through the heat transfer plate and/or the end heat transfer plates, which allows the various battery modules to be maintained at the optimal temperature.
If a plurality of cells are linked together with the elements for electromotive force of each cell provided inside a battery case in which the individual battery housings are integrally formed adjacent to one another between the short sides thereof, then the plurality of cells will be integrally structured such that the battery case common to the plurality of cells serves as the battery housings of the various cells, so the structure linking the battery housings can be formed more easily.
Also, if the plurality of cells are sandwiched between a pair of binding plates, and the pair of binding plates together are tied together, the plurality of cells can be integrally linked, and can be securely linked integrally regardless of the arrangement of the plurality of cells.
The plurality of cells can be integrally linked with the linking position and linking direction varied as desired, so that instead of being linked in a straight line, they can also be linked so as to curve in any direction, depending on the place where the rechargeable battery will be installed.
A plurality of ribs can also be formed on the sides of the battery housings, and a coolant made to flow through the spaces formed between the ribs. Coolant passages are formed between the ribs by contact between the ribs and the binding plates or between the ribs of adjacent battery housings or case, and the heat radiation of the various cells can be effectively achieved by making a coolant flow through these coolant passages.